﻿using System;

namespace GeneralUpdate.Differential.GStream
{
    public class StrangeCRC : IChecksum
    {
        private static readonly uint[] crc32Table = new uint[256]
        {
            0u, 79764919u, 159529838u, 222504665u, 319059676u, 398814059u, 445009330u, 507990021u, 638119352u, 583659535u,
            797628118u, 726387553u, 890018660u, 835552979u, 1015980042u, 944750013u, 1276238704u, 1221641927u, 1167319070u, 1095957929u,
            1595256236u, 1540665371u, 1452775106u, 1381403509u, 1780037320u, 1859660671u, 1671105958u, 1733955601u, 2031960084u, 2111593891u,
            1889500026u, 1952343757u, 2552477408u, 2632100695u, 2443283854u, 2506133561u, 2334638140u, 2414271883u, 2191915858u, 2254759653u,
            3190512472u, 3135915759u, 3081330742u, 3009969537u, 2905550212u, 2850959411u, 2762807018u, 2691435357u, 3560074640u, 3505614887u,
            3719321342u, 3648080713u, 3342211916u, 3287746299u, 3467911202u, 3396681109u, 4063920168u, 4143685023u, 4223187782u, 4286162673u,
            3779000052u, 3858754371u, 3904687514u, 3967668269u, 881225847u, 809987520u, 1023691545u, 969234094u, 662832811u, 591600412u,
            771767749u, 717299826u, 311336399u, 374308984u, 453813921u, 533576470u, 25881363u, 88864420u, 134795389u, 214552010u,
            2023205639u, 2086057648u, 1897238633u, 1976864222u, 1804852699u, 1867694188u, 1645340341u, 1724971778u, 1587496639u, 1516133128u,
            1461550545u, 1406951526u, 1302016099u, 1230646740u, 1142491917u, 1087903418u, 2896545431u, 2825181984u, 2770861561u, 2716262478u,
            3215044683u, 3143675388u, 3055782693u, 3001194130u, 2326604591u, 2389456536u, 2200899649u, 2280525302u, 2578013683u, 2640855108u,
            2418763421u, 2498394922u, 3769900519u, 3832873040u, 3912640137u, 3992402750u, 4088425275u, 4151408268u, 4197601365u, 4277358050u,
            3334271071u, 3263032808u, 3476998961u, 3422541446u, 3585640067u, 3514407732u, 3694837229u, 3640369242u, 1762451694u, 1842216281u,
            1619975040u, 1682949687u, 2047383090u, 2127137669u, 1938468188u, 2001449195u, 1325665622u, 1271206113u, 1183200824u, 1111960463u,
            1543535498u, 1489069629u, 1434599652u, 1363369299u, 622672798u, 568075817u, 748617968u, 677256519u, 907627842u, 853037301u,
            1067152940u, 995781531u, 51762726u, 131386257u, 177728840u, 240578815u, 269590778u, 349224269u, 429104020u, 491947555u,
            4046411278u, 4126034873u, 4172115296u, 4234965207u, 3794477266u, 3874110821u, 3953728444u, 4016571915u, 3609705398u, 3555108353u,
            3735388376u, 3664026991u, 3290680682u, 3236090077u, 3449943556u, 3378572211u, 3174993278u, 3120533705u, 3032266256u, 2961025959u,
            2923101090u, 2868635157u, 2813903052u, 2742672763u, 2604032198u, 2683796849u, 2461293480u, 2524268063u, 2284983834u, 2364738477u,
            2175806836u, 2238787779u, 1569362073u, 1498123566u, 1409854455u, 1355396672u, 1317987909u, 1246755826u, 1192025387u, 1137557660u,
            2072149281u, 2135122070u, 1912620623u, 1992383480u, 1753615357u, 1816598090u, 1627664531u, 1707420964u, 295390185u, 358241886u,
            404320391u, 483945776u, 43990325u, 106832002u, 186451547u, 266083308u, 932423249u, 861060070u, 1041341759u, 986742920u,
            613929101u, 542559546u, 756411363u, 701822548u, 3316196985u, 3244833742u, 3425377559u, 3370778784u, 3601682597u, 3530312978u,
            3744426955u, 3689838204u, 3819031489u, 3881883254u, 3928223919u, 4007849240u, 4037393693u, 4100235434u, 4180117107u, 4259748804u,
            2310601993u, 2373574846u, 2151335527u, 2231098320u, 2596047829u, 2659030626u, 2470359227u, 2550115596u, 2947551409u, 2876312838u,
            2788305887u, 2733848168u, 3165939309u, 3094707162u, 3040238851u, 2985771188u
        };

        private int globalCrc;

        public long Value => ~globalCrc;

        public StrangeCRC()
        {
            Reset();
        }

        public void Reset()
        {
            globalCrc = -1;
        }

        public void Update(int value)
        {
            int num = (globalCrc >> 24) ^ value;
            if (num < 0)
            {
                num = 256 + num;
            }

            globalCrc = (int)((globalCrc << 8) ^ crc32Table[num]);
        }

        public void Update(byte[] buffer)
        {
            if (buffer == null)
            {
                throw new ArgumentNullException("buffer");
            }

            Update(buffer, 0, buffer.Length);
        }

        public void Update(byte[] buffer, int offset, int count)
        {
            if (buffer == null)
            {
                throw new ArgumentNullException("buffer");
            }

            if (offset < 0)
            {
                throw new ArgumentOutOfRangeException("offset", "cannot be less than zero");
            }

            if (count < 0)
            {
                throw new ArgumentOutOfRangeException("count", "cannot be less than zero");
            }

            if (offset + count > buffer.Length)
            {
                throw new ArgumentOutOfRangeException("count");
            }

            for (int i = 0; i < count; i++)
            {
                Update(buffer[offset++]);
            }
        }
    }
}